JP2007283104A - Control method for magnetic resonance system, magnetic resonance system and computer program product - Google Patents

Control method for magnetic resonance system, magnetic resonance system and computer program product Download PDF

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JP2007283104A
JP2007283104A JP2007106180A JP2007106180A JP2007283104A JP 2007283104 A JP2007283104 A JP 2007283104A JP 2007106180 A JP2007106180 A JP 2007106180A JP 2007106180 A JP2007106180 A JP 2007106180A JP 2007283104 A JP2007283104 A JP 2007283104A
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measured value
magnetic resonance
distribution
value distribution
high
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JP5209895B2 (en
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Juergen Nistler
ニストラー ユルゲン
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Siemens Ag
シーメンス アクチエンゲゼルシヤフトSiemens Aktiengesellschaft
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00Arrangements or instruments for measuring magnetic variables
    • G01R33/20Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/32Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/34Constructional details, e.g. resonators, specially adapted to MR
    • G01R33/341Constructional details, e.g. resonators, specially adapted to MR comprising surface coils
    • G01R33/3415Constructional details, e.g. resonators, specially adapted to MR comprising surface coils comprising arrays of sub-coils, i.e. phased-array coils with fileiple receiver channels
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00Arrangements or instruments for measuring magnetic variables
    • G01R33/20Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/24Arrangements or instruments for measuring magnetic variables involving magnetic resonance for measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/246Spatial mapping of the RF magnetic field B1
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00Arrangements or instruments for measuring magnetic variables
    • G01R33/20Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48NMR imaging systems
    • G01R33/54Signal processing systems, e.g. using pulse sequences, Generation or control of pulse sequences ; Operator Console
    • G01R33/56Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/565Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/5659Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for obtaining a transmit parameter set favorable enough for an expected magnetic resonance measurement at high speed in a short adjustment time. <P>SOLUTION: Under excitation of a first transmit mode of a high-frequency antenna, a measured value distribution of a high-frequency magnetic field distribution is obtained, and concerning the evaluation reference, uniformity of the measured value distribution is evaluated. When the evaluation reference is satisfied, the transmit mode is used to perform desired magnetic resonance measurement, and if not satisfied, under the excitation of another transmit mode, the measured value distribution of a high-frequency magnetic field distribution is obtained, the measured value distribution, the uniformity of which is optimized, is calculated based on combination of the respective measured value distributions measured until the concerned point of time. Concerning the evaluation reference, uniformity of the optimized measured value distribution is evaluated, and when the evaluation reference is satisfied, magnetic resonance measurement is performed using the transmit parameter set obtained based on the calculated optimized measured value distribution. If the evaluation reference is not satisfied, the above step is repeated using still another transmit mode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for controlling a magnetic resonance system for performing a magnetic resonance measurement in at least one predetermined volume region of interest in a subject, wherein the magnetic resonance system comprises several resonant elements. The resonance element can excite various transmission modes in order to form a primary-independent high-frequency magnetic field distribution in the test volume including the subject. The invention further relates to a magnetic resonance system suitable for carrying out such a method, the magnetic resonance system comprising a high-frequency antenna as well as a computer program product, the computer program product performing this method. In order to do so, it can be stored in the memory of a programmable controller of such a magnetic resonance system.

Magnetic resonance tomography (also referred to as nuclear spin tomography) is a technique that is currently used extensively to form in-vivo images of living subjects. To form an image using this method, firstly, the body or inspection to be the body of the patient, homogeneous basic static magnetic field as possible (usually referred to as the B 0 field) is applied, the basic static magnetic field Formed by the basic magnetic field magnet of the magnetic resonance apparatus. A gradient magnetic field that is switched at high speed during magnetic resonance imaging is superimposed on the basic magnetic field for position encoding, and this gradient magnetic field is formed by a so-called gradient coil. Furthermore, a high-frequency pulse having a predetermined magnetic field strength is irradiated into the subject using a high-frequency antenna. The magnetic flux density of the high frequency pulse, commonly referred to as B 1. Pulsed RF magnetic field, therefore, is generally shortened to called B 1 field. Using this high-frequency pulse, the nuclear spins of the atoms in the subject are only called the “excitation flip angle” (generally called “flip angle” for short) from the equilibrium position state of each spin. It is polarized parallel to the basic magnetic field B 0. At that time, the nuclear spins precess around the direction of the basic magnetic field B 0. The magnetic resonance signal formed thereby is received by each high frequency receiving antenna. Each receiving antenna may be the same antenna as the antenna that emits the high-frequency pulse, or may be a separate receiving antenna. The magnetic resonance image of the subject is eventually formed based on the received magnetic resonance signal. At that time, each dot in the magnetic resonance image is assigned to a small body volume part, a so-called “voxel”, and each luminance value or intensity value of the dot is a signal of a magnetic resonance signal received from this voxel. Combined with amplitude. The relationship between the high-frequency pulse radiated at the resonance frequency (resonant) with the magnetic field strength B 1 and the flip angle α achieved thereby is obtained by the following equation (1):
In this case, γ is a gyromagnetic ratio that can be regarded as a fixed material constant in the case of most nuclear spin inspections, and τ is an operation period of a high-frequency pulse. The flip angle achieved by the delivered radio frequency pulse, and hence the strength of the magnetic resonance signal, depends not only on the pulse duration but also on the strength of the emitted B 1 magnetic field. Thus, the spatial variation of the field strength of the excited B 1 field, the received magnetic resonance signal fluctuates undesirably, thereby sometimes measurement result is deteriorated.

Disadvantageously, however, high frequency pulses with high magnetic field strength that are inevitably delivered based on the required basic magnetic field B 0 in a nuclear spin tomograph, for example, in conductive and dielectric media, such as tissue, The non-uniform permeation characteristics (Eindringverhalten) are shown. Thereby, the B 1 magnetic field inside the measurement volume may change strongly. In particular, in the ultra-high magnetic field region where the magnetic field strength B 0 ≧ 3 T, it is observed that the high-frequency penetration characteristics significantly affect the image quality. The flip angle of the high frequency pulse is a function of position due to the B 1 focusing effect and the shielding effect. Therefore, the contrast and brightness of the imaged magnetic resonance image vary within the imaged tissue, and in the worst case, the pathological structure may become invisible.

As a promising approach for solving this problem, multi-channel transmission coils, which are also called “Transmit-Arrays”, are currently being discussed. In this case, a high-frequency antenna of the type described at the beginning, including several resonant antennas and antenna elements, is used, each of which can be controlled individually or in groups, ie with different transmission configurations. It is. This is possible, for example, if the individual resonant elements are electromagnetically decoupled from each other and can be controlled with separate amplitude and phase via separate high frequency channels. Different high frequency distributions are formed in the test volume of the antenna, depending on whether different transmission configurations are excited or amplitude and phase. For example, different linear N magnetic field distributions independent of each other can be formed using an antenna having N resonant elements that are electromagnetically decoupled from each other and can be individually controlled. A simple example of this is a birdcage resonator, which can be individually controlled with respect to the amplitude and phase of the birdcage resonator. Each of these bars, independently of one another to form a B 1 field, where, B 1 field of the individual bar is superimposed to form a total one magnetic field distribution.

  Instead of considering individual resonant elements individually, different “collective excitation modes” can also be excited individually using such antennas. For control of such collective modes, also called "transmit modes" or "field modes", the output is fixed, for example, in the hardware used for antenna element control A mode matrix (eg, a Butler matrix “butler matrix”) may be installed. Alternatively, the individual antenna elements may be appropriately controlled by software.

At that time, the spatial distribution of the B 1 magnetic field is adjusted by individually adjusting the amplitude and phase of the high-frequency pulse transmitted from each transmission configuration in order to form a high-frequency magnetic field as uniform as possible in the subject or the test volume. You may make it act on. A corresponding magnetic resonance apparatus is described, for example, in U.S. Pat. No. 6,043,658 and German Offenlegungsschrift 102004045691.

From German Offenlegungsschrift 102004013422, a method and a magnetic resonance system for homogenizing the B 1 field are known. In so doing, homogenizing the B 1 field is achieved using an iterative step. During the first iteration step, measurement data indicative of a B 1 magnetic field distribution within at least a portion of the test volume is detected, with subsequent B 1 magnetic field uniformity based on the detected measurement data. Analysis is automatically performed. A predetermined homogenization operation is then automatically selected from several possible homogenization operations based on an analysis of the uniformity of the B 1 field. Subsequently, the selected homogenization operation is performed to finally make the B 1 field uniform.
US Pat. No. 6,043,658 German Patent Publication No. 102004045691 Federal Republic of Germany Patent Publication No. 102004013422

However, a problem that has not been solved so far is that transmission parameters are obtained for individual antenna elements, and as a result, a region of interest (Region of Interest, ROI) within a patient or at least for a desired imaging is obtained. In other words, the B 1 magnetic field distribution is as uniform as practically possible. Possible way for obtaining the parameter is to detect the distribution of the B 1 field with respect to the individual of each resonance element, B 1 field value and phase. At that time, it is necessary to obtain an overall image so that all the resonance elements are in an activated state. Subsequently, an optimization region (eg, ROI) needs to be determined, and control parameters are calculated for uniform excitation. However, such a measurement is very time consuming. At that time, the total adjustment time is as long as 10 minutes. Therefore, this method is actually not very suitable as an adjustment method.

  Accordingly, an object of the present invention is to provide means for obtaining a sufficiently good transmission parameter set for an intended magnetic resonance measurement at high speed, that is, with a small adjustment time.

This problem is solved by the method of claim 1, the magnetic resonance system of claim 11 and the computer program product of claim 12. According to the invention, the following method steps are performed for this purpose:
a) First, a measured value distribution indicating a high-frequency magnetic field distribution in a predetermined volume region is obtained under excitation of the first transmission mode. This measured value distribution is advantageously a flip angle distribution. As described above, the flip angle α measured at the predetermined position is shown with respect to the B 1 magnetic field irradiated at the predetermined position, and the dependency is shown according to the equation (1). That is, (if you know the used pulse) using this equation, optionally, converted from flip angle distribution in B 1 field distribution, optionally, converted from the B 1 field distribution in flip angle distribution.
b) The uniformity of the measured value distribution in the predetermined volume region is evaluated in the first transmission mode with respect to a predetermined evaluation criterion determined in advance. When the evaluation criteria are satisfied at the time of transmission in the first transmission mode, a desired magnetic resonance measurement can be performed immediately using the first transmission mode. That is, at that time, the parameters necessary for exciting the first transmission mode are used as the transmission parameter set.

However, if the evaluation criteria are not met, the following separate steps are performed:
c) In this case, in order to determine again the measured value distribution indicating the high-frequency magnetic field distribution for this transmission configuration within a given volume region, another (instead of the previously excited transmission mode) The high frequency antenna is excited in the transmission mode. In this case, the measured value distribution is determined in accordance with the measured value distribution determined in step a). For example, a flip angle distribution is also determined in this case.
d) Subsequently, a measured value distribution optimized for uniformity within a predetermined volume region is calculated based on each measured value distribution measured in various transmission modes up to that point in time.
e) For a given evaluation criterion, the uniformity of the optimized measurement value distribution calculated within a given volume region is determined. If the evaluation criterion is satisfied, an optimized transmission parameter set is obtained based on the optimized measurement value distribution previously calculated in step d), and the optimized transmission parameter set is used. Thus, the desired magnetic resonance measurement can be performed. If the evaluation criteria are still not satisfied at this point, steps c) to e) are repeated using another transmission mode.

  The method of the present invention is based on the duality of consideration of individual resonant elements and collective transmission modes. That is, on the other hand, the transmission mode is represented by each current distribution of all the resonant elements. On the other hand, the current on the resonant element can also be represented by a combination of a plurality of transmission modes. Instead of measuring the magnetic field distribution for individual resonant elements, the magnetic field distribution is measured for individual collective transmission modes, and the uniformity is adjusted in a continuous manner when using this method. Several steps for this and therefore the adjustment time can be clearly reduced. This is in particular that not all transmission modes contribute equally for uniformity. Therefore, the method should advantageously start in the mode that has the strongest impact on uniformity. In the most advantageous case, according to the method of the present invention, if the uniformity is already good enough, one transmission mode is sufficient for the measurement. In the worst case, it may take a great deal of time to fully measure all the individual resonant elements and make the adjustments necessary to determine the optimal set of transmission parameters from that measurement.

The magnetic resonance system of the present invention can be used in various ways to form independent linear high-frequency distributions in addition to the above-described high-frequency antenna and the antenna control device including several resonance elements that can be controlled individually or in groups. In order to excite the resonant element in different transmission modes, it has the following other components:
A measurement value distribution detection unit for obtaining a measurement value distribution indicating a high frequency magnetic field distribution in at least one volume region inside the subject under excitation of a predetermined transmission mode of the high frequency antenna;
-An evaluation unit for automatically evaluating the uniformity of the measurement value distribution within the volume region with respect to a given evaluation criterion;
A combination unit for calculating a measured value distribution optimized for uniformity within a given volume region based on a combination of each measured value distribution measured in different transmission modes;
And each of the above-described method steps a) to perform the magnetic resonance measurement in the at least one predetermined volume region inside the subject by the antenna control device, the measurement value distribution detection unit, the evaluation unit and the combination unit. a measurement sequence control unit for performing e).

  The antenna controller, the measurement value distribution detection unit, the evaluation unit, the combination unit and the measurement sequence control unit are advantageously integrated, at least in part, into a normal system controller used for the control of the magnetic resonance system. Has been. The antenna controller, the measurement value distribution detection unit, the evaluation unit, the combination unit and the measurement sequence control unit may be made up of a number of parts, for example integrated into very different components of the system controller It may be configured from various different modules. Advantageously, the antenna control program module, the measurement value distribution detection program module, the evaluation program module, the combination program module or the measurement sequence control program module, which can be called up in the computer-aided control device of the magnetic resonance system Configured in the form of software modules. A computer-aided control device is here a control device equipped with a suitable processor and other components in order to execute a provided control program, measurement program and / or calculation program.

  The dependent claims each include particularly advantageous embodiments or embodiments of the invention, in which case the magnetic resonance system of the invention is implemented in the same way as the requirements of the independent claims of the method of the invention. be able to.

  As described above, each mode all contributes to uniformity as well. Instead, the gain in uniformity is specified in particular by a relatively low transmission mode, i.e. a relatively low order transmission mode, and only slightly improved in a relatively high transmission mode. Therefore, in an advantageous embodiment of the invention, the basic transmission mode of the high-frequency antenna is used as the first transmission mode, and each of the immediately following is determined when the measured value distribution is subsequently determined in step c) above. A higher transmission mode, i.e., the next highest order transmission mode, is excited in the high frequency antenna. In this way, the method can be made even faster. In general, for an antenna with eight resonant elements, four measurement steps are sufficient even if it is disadvantageous.

  In order to obtain an optimized measurement distribution on the basis of the combination of the respective measurement value distributions measured in the various transmission modes up to that point in step d) of the method, it is advantageous to use the first order of the different measurement value distributions. A combination is formed, in which the first-order combination of each measured value distribution is weighted with respect to the various transmission modes, particularly preferably with respect to the amplitude and the phase of the transmission mode.

  Advantageously, the amplitude parameter may then be limited, for example in order to control the load of individual components or the local SAR (Specific Absorption Ratio). In other words, for this purpose, a predetermined SAR limit value can be maintained without exceeding a predetermined load limit.

  Very different criteria can be used for the assessment of uniformity. A possible criterion is an evaluation of the measured value in the selected area, for example the standard deviation of the flip angle. For this purpose, for example, a limit standard deviation is set, and if the standard deviation of the measured value distribution is below this limit standard deviation, the evaluation criterion is considered to be satisfied.

  In another advantageous embodiment, when measuring the uniformity of the measurement distribution, it is checked whether a local measurement (eg flip angle) falls below or exceeds a predetermined limit value within a predetermined volume region. The

  Alternatively, one value derived from one local measurement value, in particular a relative value, i.e. a local measurement within a slice, in a given volume region when evaluating the uniformity of the measurement value distribution. It may be checked whether the ratio of the value and the averaged measured value is below or exceeds a predetermined limit value.

  Similarly, different methods may be combined, i.e., sufficiently uniform, e.g., only if the standard deviation and the absolute and relative measurements are within predetermined limits. Considered.

  Since only a limited number of primary independent transmission modes are used (the same as the number of resonant elements), even when all transmission modes are considered in individual cases, the set uniformity evaluation criteria are not satisfied. Of course it cannot be excluded. Thus, if the evaluation criterion is not satisfied after excitation of all different transmission modes that can form a first-order independent high-frequency distribution, it is advantageously calculated at the last execution of step d) above. A transmission parameter set is obtained based on the optimized measurement value distribution. Thus, in this way, the best transmission parameter set that can be achieved in a specific case is identified. A desired magnetic resonance measurement can then be performed using this determined transmission parameter set.

  Advantageously, in such a case, a corresponding alarm message is sent to the operator of the magnetic resonance system, so that this operator does not meet the predetermined uniformity criteria but does not meet the best possible transmission parameter set. It can be seen that is selected.

  In doing so, at the operator's discretion, the measurement is carried out, or in some cases interrupted, or evenly within the measuring volume, for example by means of suitable auxiliary means such as a dielectric cushion or similar member. Can improve sex.

  Advantageously, prior to performing the original measurement, a corresponding confirmation by the operator is expected, in which case the operator can also indicate the determined optimized transmission parameters.

Embodiments of the present invention will be described below with reference to the drawings. In this case, the same reference numerals are assigned to the same components in the respective drawings. that time:
FIG. 1 is a flow chart for explaining a possible course of the method of the invention,
FIG. 2 shows the current distribution on each bar of a birdcage antenna with a total of 8 bars for the first four modes;
FIG. 3 shows a principle diagram of the magnetic resonance apparatus of the present invention.

  A possible measurement, evaluation and calculation process according to a variant embodiment of the method of the invention is illustrated in FIG.

In step 1, first, the flip angle distribution in the region of interest is measured in the first transmission mode M1. For birdcage antenna with eight bars, in FIG. 2, the current distribution in the first mode M 1 (diagram a) they are shown. In this case, the current (in relative units) is described over the individual bars 1-8. As can be clearly seen from FIG. 2, current distribution is performed in the first mode M 1 , the basic mode, and as a result, one current cycle is accurately distributed over eight bars. That is, as shown in the figure, in the first and fifth bars, within the phase in which no current is supplied, the maximum value of the current is supplied by the third and seventh bars, and the numbering of the bars is Arbitrary. Using such a resonator with N = 8 bars, basically N = 8 different linear independent transmission modes can be formed, with each mode and each bar being The correspondence with the current is as follows.
that time
k = 0, ..., Nl (3)
Bar numbering is
m = − (N / 2 + 1)..., 0,... (N / 2) (4)
The mode number and j specify the imaginary part.
The fundamental mode M 1 with m = 1, shown in diagram a of FIG. 2, provides a magnetic field that forms a uniform magnetic field on the unloaded antenna. This corresponds to the excitation selected as usual. Another higher mode produces a corresponding higher order current distribution in each bar. The modes M 2 , M 3 , M 4 for m = 2, m = 3 and m = 4 are illustrated in the diagrams b) to d) of FIG. Each of these modes M 2 , M 3 , M 4 can be used to improve uniformity. The mode m = 0 and the negative mode generally does not contribute to improving the uniformity in such an 8-bar-birdcage-antenna, or contributes very little.

  Various methods for measuring the flip angle distribution in step I are known to those skilled in the art. In the method of the present invention, it is basically good to use a very simple gradient echo method, which operates at a relatively high speed. At that time, the inside of the subject may be measured three-dimensionally or may be measured two-dimensionally in a slice shape.

  In Step II, the original region of interest ROI is identified therefrom, and a uniformity criterion is determined for this region. At this point, determining the region of interest ROI has the advantage that the flip angle distribution measured in step I can be used to define the region of interest ROI. However, basically, a region of interest is selected in advance before step I, and in some cases, the flip angle distribution in step I is recorded only in this region or in a peripheral region including this region. It may be.

In step III, it is checked whether the uniformity criterion defined in step II is satisfied within a given region of interest ROI. If the uniformity criterion defined in step II is satisfied within a given region of interest ROI, then in step IV the corresponding parameter set for the excitation of the first mode M 1 is the original magnetic resonance imaging. Can be used to start the measurement.

  Otherwise, in step V it is checked whether the operating variable i corresponds to the maximum number of transmission modes used, ie the number N of resonant elements.

  If the uniformity criterion defined in step II is not satisfied within a given region of interest ROI, then in step VI, the actuation variable i is incremented by 1, and then in step VII the next higher mode flip. The angle distribution is measured. That is, at the first execution, for example, as shown in the diagram b) of FIG. 2b, the measurement of the flip angle distribution in the step VII of the second mode M2 is performed.

Subsequently, in step VIII, the optimal flip angle distribution, measurement of the far, i.e., at the time of initial execution, are calculated from the measurements in both modes M 1 and M 2. At this time, a linear combination of flip angle distributions is simply formed. In this case, amplitude weighting and phase weighting can be obtained by the flip angle distribution for each mode at the time of superposition. Additionally, the component is not heavily loaded and the amplitude parameter is prevented from exceeding a predetermined limit value in order to maintain the local SAR limit value.

Then, in step VIII, in the case of this calculated optimized flip angle distribution, whether or not the uniformity criterion defined for the given region of interest ROI is satisfied in step II. Inspected. If, in step II, the uniformity criteria defined for a given region of interest ROI are fulfilled, immediately in step IV, optimized parameter sets are determined, which are then obtained by magnetic resonance imaging. Must be used in order to be able to achieve a correspondingly optimized uniform B 1 field. This is straightforward because the parameters previously determined in step VIII can be used to calculate the optimized flip angle distribution. That is, various amplitudes and phases are known in advance from this calculation.

In step III, if the criterion is still not satisfied, in step V, it is checked again whether the operating variable i has reached the number of possible modes N and the operating variable i has reached the number of possible modes N. If not, in step VI, the operating variable i is incremented by 1, and in step VII in the next height mode, for example in the third mode M 3 illustrated in diagram c) of FIG. 2d. A new measurement is performed.

  Subsequently, the calculation is again performed in step VIII, where the three flip angle distributions are linearly superimposed, and then again in step III, the uniformity evaluation for the currently optimized flip angle distribution. Inspected if criteria are met.

  This method continues until a distribution is found that satisfies the uniformity optimization criteria, or in step V, it is detected that all transmission modes are within the calculated optimal flip angle distribution. The In this case, at step IX, the operator is informed about the failure to meet the uniformity criteria, and then at step VI, the parameter set based on the last calculation at step VIII is identified. That is, in the end, the best possible parameter set is sought for this case.

  Instead of the total number N of possible modes, a smaller number may be set that corresponds to the number of modes that can contribute meaningfully to improve uniformity.

  FIG. 3 shows a simple principle block diagram of an embodiment of a magnetic resonance system 1 capable of carrying out the method of the invention.

  The core of the magnetic resonance system 1 is an imaging device 2 called a “tomograph” or “scanner” in which a patient 0 is arranged on a bed 3 in an annular main field magnet. A high frequency antenna 5 for transmitting MR high frequency pulses is provided in the main field magnet. At this time, the antenna 5 is formed of N resonant elements 6 that can be individually controlled with high-frequency pulses. At this time, for example, an antenna configuration as described in US Pat. No. 6,043,658 or German Patent Publication No. 102004045691 may be used. The tomograph further has a normal gradient coil (not shown) to deliver gradient pulses suitable for position encoding.

  Here, the tomograph 2 is controlled by the system controller 10 shown separately. An instruction device 8 for operating a graphic user interface, for example, a terminal 7 having a mouse 8 and a mass memory 9 are connected to the system control device 10. The terminal 7 is used as a user interface for an operator to operate the system controller 10 and thus the tomograph 2. The mass memory 9 is used for storing, for example, an image recorded using a magnetic resonance system. The terminal 7 and the memory 9 are connected to the system control apparatus 10 via the interface 19. The system controller 10 has a tomograph interface 11, which is connected to the tomograph 2 and has the appropriate amplitude and individual resonant elements according to the measurement sequence protocol supplied by the system controller. A high-frequency pulse having a phase for 6 and an appropriate gradient pulse are transmitted.

Further, the system control apparatus 10 is connected to the tomograph 2 via the data collection interface 12. The measurement data coming from the tomograph 2 is collected via the data collection interface 12 and assembled into an image in the signal evaluation unit 13, and then the image is displayed on the terminal 7, for example via the interface 19, and / or Alternatively, it is stored in the memory 9. One component of the signal evaluation unit 13 is here a flip angle detection unit 15, which forms a simple image of the flip angle distribution in order to display the B 1 magnetic field that has been formed. This flip-angle distribution is thus also displayed on the terminal 7 and the operator can use the mouse 8, for example, to determine the region of interest ROI that needs to satisfy the selected uniformity criterion. it can.

  Both the system controller 10, the terminal 7, and the memory 9 may be integrated components of the tomograph 2. Similarly, the system control apparatus 10 may be composed of a plurality of individual components. In particular, for example, the antenna control device 14 may be configured as a separate unit connected to the system control device 10 via a suitable interface.

  The total magnetic resonance system 1 is further interfaced with all other normal components or terminals to a communication network such as a picture information system (Picture Archiving and Communication System, PACS). It has the following features. Each of these components, however, are not shown in FIG. 3 for clarity.

  An operator can communicate with the measurement sequence control unit 18 in the system control device 10 via the terminal 7 and the interface 19. Thereby, an appropriate pulse sequence is supplied to the antenna control device 14 and the gradient control device 20 (the gradient is appropriately controlled thereby). That is, the measurement sequence control unit 18 is provided for transmitting an appropriate high-frequency pulse sequence via the antenna 5 and for appropriately switching the gradient in order to perform a desired measurement.

As described above, the signal evaluation unit 13 (configured here as a submodule) includes the flip angle distribution detection unit 15. Then, the detected flip angle distributions F 1 , F 2 , F 3 , F 4 ,. . . Can be transmitted to the evaluation unit 16 and / or the combination unit 17. The signal evaluation unit 13 to the flip angle distribution detection unit 15 as well as the combination unit 17 and the evaluation unit 16 are controlled in the same manner as the antenna control unit device 14 and the gradient control device 20 of the measurement sequence control unit 18.

This measurement sequence control unit 18 in particular has a predetermined transmission mode M 1 , M 2 , M 3 , M 4 ,. . Flip angle distributions F 1 , F 2 , F 3 , F 4 ,. . . For the measurement of the corresponding parameter sets PS 1 , PS 2 , PS 3 , PS 4 ,. . . Can be transmitted to the antenna control unit device 20, which then controls the antenna 5 accordingly via the tomograph interface 11 to transmit modes M 1 , M 2 , M 3 , M 4. ,. . . Are predetermined parameter sets PS 1 , PS 2 , PS 3 , PS 4 ,. . . To be sent by. That is, the measurement sequence control unit 18 starts the measurement in one measurement sequence, and as a result, the predetermined transmission modes M 1 , M 2 , M 3 , M 4 ,. . . Flip angle distributions F 1 , F 2 , F 3 , F 4 ,. . . Can be recorded by the flip angle distribution detection unit 15. Then each mode M 1 , M 2 , M 3 , M 4 ,. . . Measured flip angle distributions F 1 , F 2 , F 3 , F 4 ,. . . Is transmitted from the flip angle distribution detection unit 15 to the evaluation unit 16 and the combination unit 17.

Then, after the control unit of the corresponding by measurement sequence control unit 18, for example, at the time of measurement of the first transmission by step I mode M 1 of Fig. 1, the evaluation unit 16, the evaluation in step III of FIG. 1 is performed. The result is supplied to the measurement sequence control unit 18. If this result is satisfactory, the measurement sequence control unit 18 transmits the optimized parameter set PS 0 found to the antenna controller 14 and thus using this parameter set PS 0 The signal evaluation unit 13 can form a desired magnetic resonance image using the obtained signal.

If the evaluation criteria are not met, the measurement sequence control unit 18 starts the measurement in the second transmission mode M 2 by transmission of another parameter set PS 2 , and subsequently the measurement value distribution detection unit 15 The flip angle distribution F 2 is measured, and this flip angle distribution F 2 is similarly transmitted to the combination unit 17. The combination unit 17 then combines the flip angle distribution F 2 with the pre-measured flip angle distribution F 1 and forwards the result, ie the combined flip angle distribution F K, to the evaluation unit 16. The evaluation unit 16 evaluates the flip angle distribution F K as described above, and supplies the measurement sequence control unit 18 the result again. If the result is satisfactory, the measurement sequence control unit unit hand 18 determines from the optimized combination of each flip angle distribution F 1 , F 2 based on the data supplied by the combination unit 17 An optimized parameter set PS 0 is formed, and the original antenna control device 14 for measurement is controlled using the optimized parameter set PS 0 .

Also utilized the last transmission mode, if satisfactory result is not achieved, the measurement sequence control unit 18 receives the necessary data from the combination unit 17, to form a good parameter set PS K as possible at least, then , the parameter set PS K, is transmitted to the antenna control unit 14 for subsequent magnetic resonance measurement. At the same time, an alarm instruction to the operator can be output to the terminal 7 via the interface 19.

  In general, at least the measurement sequence control unit 18, the signal evaluation unit 13, the flip angle distribution detection unit 15, the combination unit 17 and the evaluation unit 16 are configured on the processor of the system controller 10 in the form of a software module. . The advantage of purely software configuration is that existing magnetic resonance apparatus can be upgraded later with corresponding software upgrades. At this time, the units 13, 15, 16, 17, 18, and the corresponding software modules shown as individual blocks in FIG. 3 may be composed of a plurality of components or subroutines. In this case, each of these subroutines may be already used by another component of the system control apparatus 10, that is, in some cases, an existing subroutine of another program unit may be used. Costs may be kept as low as possible when executing modules essential to the invention.

In summary, the present invention describes a method for controlling the MR system 1 to perform a magnetic resonance measurement within a predetermined volume region. The MR system 1 has different transmission modes M 1 , M 2 ,. . . A high-frequency antenna 5 having a resonance element 6 that can be excited by the For this, the following steps are performed:
a) obtaining a measured value distribution F 1 indicating the high-frequency magnetic field distribution in a predetermined volume region under excitation of the first transmission mode M 1 of the high-frequency antenna 5;
b) evaluating the uniformity of the measurement value distribution F 1 with respect to a predetermined evaluation criterion, and executing the desired magnetic resonance measurement using the first transmission mode M 1 if the evaluation criterion is satisfied Or if the evaluation criteria are not met,
a) Different transmission modes M 2 , M 3 , M 4 ,. . , Measured value distributions F 2 , F 3 , F 4 ,. . A step of seeking
d) Measured value distributions F K optimized for homogeneity are represented by respective measured value distributions F 1 , F 2 , F 3 , F 4 ,. . . Calculating based on a combination of
regard e) a predetermined criterion, at a given volume area, and a step of evaluating the uniformity of the optimized measured value distribution F K, if the criteria are met, the optimized calculated in step d) If the transmission parameter set PS 0 is obtained based on the measured value distribution F K and the magnetic resonance measurement is performed using the transmission parameter set PS 0 or the evaluation criterion is not satisfied, A step of repeating steps c) to e) using the transmission mode is executed.

  The method described in detail above and the illustrated magnetic resonance system is merely one example, which can be modified in various ways by those skilled in the art without departing from the scope of the present invention. be able to.

  The present invention has been described mainly by using an example used in a magnetic resonance apparatus useful in the medical field. However, such applications are in no way limiting and may be used in scientific and / or industrial applications.

2 is a flow diagram for explaining a possible course of the method of the present invention. The figure which shows the electric current distribution on each bar | burr of the birdcage-type antenna provided with a total of 8 bar | burrs for 1st four modes. The principle figure of the magnetic resonance apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic resonance system 2 Tomograph 5 Antenna 6 Resonance element 7 Terminal 8 Indication apparatus for operation of graphic user interface, for example, mouse 9 Mass memory 10 System controller 11 Tomograph interface 12 Data acquisition interface 13 Signal evaluation unit 14 Antenna controller 15 Flip Angle detection unit 16 Evaluation unit 17 Combination unit 18 Measurement sequence control unit 19 Interface 20 Gradient control device

Claims (12)

  1. A method of controlling a magnetic resonance system (1) for performing a magnetic resonance measurement in at least one predetermined volume region in an object (O), the magnetic resonance system (1) comprising several resonances A high-frequency antenna (5) having an element (6) is provided, and the resonance element forms a primary-independent high-frequency magnetic field distribution in a test volume (4) including the subject (O). In order to be able to excite the various transmission modes (M 1 , M 2 , M 3 , M 4 ,...)
    a) obtaining a measured value distribution (F 1 ) indicating a high-frequency magnetic field distribution in a predetermined volume region under excitation of the first transmission mode (M 1 ) of the high-frequency antenna (5);
    b) evaluating a uniformity of the measured value distribution (F 1 ) within the predetermined volume region with respect to a predetermined evaluation criterion; and if the evaluation criterion is satisfied, the first transmission mode ( Performing a desired magnetic resonance measurement using M 1 ), or if the evaluation criteria are not satisfied,
    c) A measured value distribution (F 2) showing a high-frequency magnetic field distribution in a predetermined volume region under excitation of another transmission mode (M 2 , M 3 , M 4 ,...) of the high-frequency antenna (5). , F 3 , F 4 ,.
    d) optimized measured value distribution with respect to the uniformity in the predetermined volume in the region (F K), various transmission modes until the point (M 1, M 2, M 3, M 4, ... ) Based on the respective measured value distributions (F 1 , F 2 , F 3 , F 4 ,...) Measured in
    e) evaluating the uniformity of the optimized measurement value distribution (F K ) calculated within the predetermined volume region with respect to the predetermined evaluation criterion, and if the evaluation criterion is satisfied,
    Based on said step d) is optimized and calculated in the measurement value distribution (F K), optimized transmission parameters set (PS 0) the calculated and the optimized transmission parameters set (PS 0) To perform the desired magnetic resonance measurement, or
    Alternatively, when the evaluation criterion is not satisfied, the control further includes a step of repeating the steps c) to e) by using another transmission mode (M 2 , M 3 , M 4 ,...). Method.
  2. The first transmission mode (M 1 ) is a basic transmission mode of the high-frequency antenna (5). Subsequently, in step c), the measured value distribution (F 2 , F 3 , F 4 ,. The control method according to claim 1, wherein, when obtaining, the high frequency antenna is excited with one next highest transmission mode (M 2 , M 3 , M 4 ,...).
  3. In step d), the measured value distribution (F K ) optimized for uniformity is measured in various transmission modes (M 1 , M 2 , M 3 , M 4 ,. 3. The control method according to claim 1, wherein the control method is based on a linear combination of (F 1 , F 2 , F 3 , F 4 ,...).
  4. Each measured value distribution (F 1 , F 2 , F 3 , F 4 ,...) Of various transmission modes (M 1 , M 2 , M 3 , M 4 ,. 4. The control method according to claim 3, wherein the weighting is sometimes performed with respect to the amplitude of the transmission mode.
  5. Each measured value distribution (F 1 , F 2 , F 3 , F 4 ,...) Of various transmission modes (M 1 , M 2 , M 3 , M 4 ,. The control method according to claim 3 or 4, wherein weighting is sometimes performed with respect to a phase of the transmission mode.
  6. Measured distribution of a given volume area (F 1, F 2, F 3, ..., F K) Evaluation of uniformity of the measurement value distribution (F 1, F 2, F 3, .. , F K ), the control method according to any one of claims 1 to 5.
  7. Whether the local measurement value falls below or exceeds a predetermined limit value within a predetermined volume region when evaluating the uniformity of the measurement value distribution (F 1 , F 2 , F 3 ,..., F K ) The control method according to claim 1, wherein the control method is inspected.
  8. When evaluating the uniformity of the measurement value distributions (F 1 , F 2 , F 3 ,..., F K ), one value derived from one local measurement value is a predetermined limit value within a predetermined volume region. A control method according to any one of claims 1 to 7, wherein it is inspected whether the value is below or exceeded.
  9. If the evaluation criteria are not satisfied after excitation of all the various transmission modes (M 1 , M 2 , M 3 , M 4 ,...) That can form a primary independent high-frequency magnetic field distribution A set (PS K ) is determined based on the optimized measured value distribution (F K ) calculated at the time of the last execution of the step d), and a desired value is set using the transmission parameter set (PS K ). The control method according to claim 1, wherein magnetic resonance measurement is performed.
  10. If the evaluation criteria are not satisfied after excitation of all the various transmission modes (M 1 , M 2 , M 3 , M 4 ,...) That can form a primary independent high-frequency magnetic field distribution, magnetic resonance 10. The control method according to claim 1, wherein a warning message (W) is sent to an operator of the system (1).
  11. In the magnetic resonance system (1),
    A high-frequency antenna (5), an antenna control device (14), a measurement value distribution detection unit (15), an evaluation unit (16), a combination unit (17), and a measurement sequence control unit (12) The high-frequency antenna (5) has several resonant elements (6) that can be controlled individually or in groups,
    The antenna control device (14) excites the resonance element (6) in various transmission modes (M 1 , M 2 , M 3 , M 4 ,...) And includes a subject (O). A primary independent high-frequency magnetic field distribution is formed in the test volume unit (4), and the measurement value distribution detection unit (15) generates a high-frequency magnetic field distribution in at least one volume region in the subject (O). The measured value distributions (F 1 , F 2 , F 3 , F 4 ,...) Shown are represented by the predetermined transmission modes (M 1 , M 2 , M 3 , M 4 ,. The evaluation unit (16) determines the uniformity of the measured value distributions (F 1 , F 2 , F 3 , F 4 ,...) Within the volume region according to a predetermined evaluation. Evaluate with respect to standards,
    The combination unit (17) is configured such that each of the measured value distributions (F 1 , F 2 , F 3 , F) measured in the various transmission modes (M 1 , M 2 , M 3 , M 4 ,...). 4 ,...) Based on the combination of the measured value distribution (F K ) optimized within the predetermined volume region, the measurement sequence control unit (12) The device (14), the measurement value distribution detection unit (15), the evaluation unit (16), and the combination unit (17) are controlled so as to be within the at least one predetermined volume region in the subject (O). Is configured to perform the following method steps to perform a magnetic resonance measurement at:
    a) obtaining a measured value distribution (F 1 ) indicating the high-frequency magnetic field distribution within the predetermined volume region under excitation of the first transmission mode (M 1 ) of the high-frequency antenna (5);
    b) evaluating the uniformity of the measured value distribution (F K ) within the predetermined volume region with respect to the predetermined evaluation criterion; and if the evaluation criterion is satisfied, the first transmission mode Performing a desired magnetic resonance measurement using (M 1 ), or if the evaluation criteria are not satisfied,
    c) A measured value distribution (F 2) showing a high-frequency magnetic field distribution in a predetermined volume region under excitation of another transmission mode (M 2 , M 3 , M 4 ,...) of the high-frequency antenna (5). , F 3 , F 4 ,.
    d) The measured value distribution (F K ) optimized for the homogeneity within the predetermined volume region is transferred to the various transmission modes (M 1 , M 2 , M 3 , M 4 ,. .) Based on the respective measured value distributions (F 1 , F 2 , F 3 , F 4 ,...)
    e) evaluating the uniformity of the optimized measurement value distribution (F K ) calculated within the predetermined volume region with respect to the predetermined evaluation criterion; and when the evaluation criterion is satisfied, Based on the optimized measurement value distribution (F K ) calculated in step d), an optimized transmission parameter set (PS 0 ) is obtained, and the optimized transmission parameter set (PS 0 ) is obtained. To perform the desired magnetic resonance measurement, or
    Alternatively, when the evaluation criterion is not satisfied, the method further includes the step of repeating the steps c) to e) by using another transmission mode (M 2 , M 3 , M 4 ,...). Resonance system (1).
  12.   When the program is executed on the control device (10) of the magnetic resonance system (1), using program code means to carry out all the steps of the method according to any one of claims 1 to 10, A computer program product that can be stored directly in the memory of the programmable controller (10) of the magnetic resonance system (1).
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